1. Field of the Invention
The present invention relates to a control for an internal combustion engine and more particularly an engine control based on engine roughness.
2. Description of the Prior Art
In modern automobile engines, the fuel supply to the engine is controlled so that the air-fuel mixture be made as lean as possible to thereby improve fuel economy. It should however be noted that, if the mixture is excessively lean, there will be produced an uncomfortable engine roughness caused by torque fluctuations due to misfire. It is therefore desirable in the field of engines to improve that fuel economy while suppressing the torque fluctuations.
In Japanese utility model application No. 56-257 filed on Jan. 7, 1981, and disclosed for public inspection on July 15, 1982, under the disclosure number 57-114141, there is disclosed an engine control system including a torque fluctuation detecting device for detecting engine torque fluctuations, and a comparing device for comparing the torque fluctuation signals from the torque fluctuation detecting device with a reference value so that the fuel supply to the engine is decreased when the torque fluction signals are below the reference signal, but the fuel supply is increased when the torque fluctuation signals are greater than the reference signal to thereby decrease the torque fluctuations. With this control, it is possible to suppress the engine torque fluctuations to a minimum level with the fuel supply maintained as low as possible.
It should, however, be pointed out that the engine torque fluctuation, that is, the engine roughness level, changes depending on the engine operating conditions, such as the load on the engine and the engine temperature. For example, the roughness level is higher under loaded engine operation than under an idling operation. Further, the roughness level increases as the engine load increases. Despite these facts, if the reference signal is fixed to a value which is appropriate for obtaining a desired result under an idling operation, there will be a tendency that the fuel supply is increased under loaded operation due to an increase in the roughness level.